Electric-current transmission



' June 12, 1,928.

D. F. WHITING ELzcrRIc CURRENT TnmsmssIon Fi led llay 28, 192s{Sheets-Sheet '1 lnven/orx Dana/d E Whlling. by r June 12,1928.1,672,995 D. F. .WHITING zwcmc 0mm TRANSMISSION Fil'ed lay 28, 192:5 2Sheets-Sheet 2 Q Miles gaih V I Cycles persecond I 1 1 1 1 1 l 1 Q 200 I100 600 800 I000 I200 I400 I600 /800 2000 2200 2100 2000 800 .7000

Cycles per second I l l I l l ll I l 200 1m @00- $00 AW #00 I009 QM Z0002200 100 2500 300 transformer to raise the I Patented dune 12, 1928 YUNITED STATES PATENT,

ojrricsl] V DONALD I. WRITING, 01' NEW YORK, N. Y., ASSIGNOB WC mun,moonronn'rnn, or saw You, N. Y., a oonromnox or You.

nnc'rmc-ctmnm'r TBANBIISSION. V Application fled Kay 88, 1923. Serial.10. 641,840.

r This invention relates to transmitting electric currents, especiallyto repeating telephone currents, and aims to accomplish such repeatingefliciently and without undue distortion. i

In accordance with the invention the transmission characteristics of anelectron tube repeater or the like are controlled preferably byproviding inductance effectively in series in the input circuit of therepeater and so arranging a condenser in the repeater input circuit asto provide capacity effectivel across the input circuit, the inductanceten ing toresonate with the tube capacity and the capacity between thewinding turns of the gain frequency curve of the repeater at the higherfrequencies to be transmitted, and the capacity of the condensercooperatin Y with the inductance to give the desired Snipe of this partof the curve. For instance, in case the adjustment of "the inductance toraise thispart of the curveto the desired do for one gain setting of therepeater ten sto cause an unduly large rise for another gain settin ofthe repeater, the condenser may be use to ,prevent such undue rise. Thedifferent settingsof the repeater may be obtainecf l i y employingbetween-the incoming line and the input terminals of the amplifier a.device having a variable ratio of input voltage to output voltage, asfor example, an input transformer having taps on its secondary winding;and the condenser may be so arranged as to provide capacity connectedeffectively across the secondary;

winding of the transformer by adjustment of the transformer from onegain setting to another, as for instance from a hi her to a lower gainsetting. This action 0 the condensermay serve to compensa e forvariations in the. effect of the tube capacity upon the repeater gain as thegain setting is changedi effective y in series in the input circuit ofthe repeater to resonate with the tube ca-' pacity or not. A Fig. 1 ofthe accompanying drawingsis a circuit diagram of one embodiment of theinvention; Figs. 2 and 3 are curves for facilit'ating explanation oftheinvention; Figs. 4, 5, 61nd are circuit diagrams'illustratingmodifications of the form of the invention shown in Fig. 1; and Fig. isan elevation at one type f structure whlch m yem dy whether -.inductanceis inserted transformer is made su an effective leakage inductance ofapproxithe transformer and compensating condenser 1, 4, 5 or 6.

of I a In. ig. 1, currents such for exam le as speech frequency currentsare repeate from a line 11- to a line 12 by means of an electron tubeamplifier 13. The line 11 is preferably terminated by a resistance 14 '0apmately the value of inductance 17, this leakage inductance may servethe purpose of the inductance 17 The secondary winding 19 of the in uttransformer has p conductors 1 to 9, tie tap conductor 1 bei g connectedto the cathode of the tube 13, t e control electrode or lgrid of whichmay be connected to any of t e tap conductors by means of an cientlygreat to give adjustable contact 20 at the end of 's'conductor 21leading from the grid (all after the fashion disclosed and. claimed in tMathes Patent No. 1,495,422, issued May 27, 1924). A condenser 25 ispreferably con- .nected between the tap conductor 9 and the grid, forreasons appearing hereinafter, and

"an output transformer 31 is preferably incable,

ter posed between the tube 13 and the line 12. he curves of F i 2 areobserved gain frequency curves, 0 the repeater for different settings ofthe contact 20, all of these curves having been taken with theinductance 17 and condenser 25 out of circuit, and

all of these curves except the cur've9 for tap 9 having been taken withthe condenser'18 in circuit, Curves 2,13, 4, 5, 6, 7, 8 and 9 correspondto the taps of the same numbers, respectively. The ordinates of thecurves give the gain in terms of miles of standard "The curves of Fig. 3are corresponding observed gain frequency curves of the repeater withthe inductance 17 and the condensers 18 and 25 in-circuit, the capacityof the condenser25having been maintained at a constantvalue of mmf. Theinduc nee- 17 was 13 milhenries, the capacitg 18 as M nt, smiths tube 13was type 1 l -B an I \Vestern Electric vacuum tube. The impedances ofline 11, resistance 14 and line 12 were 900 ohms, 900 ohms and 700 ohmsrespectively, the impedance ratio of the step up transformer 16 was909:600,000 for the highest gain setting and the ratio of transformer 31was 6,000:7GO. Curves 2, 3, 1, 5, 6, 7",8 and 9' correspond to taps 2,3, 1, 5, 6. 7, 3 and 9 respectively.

Considering now the action of the repeater of Fig. 1 in its highest gainsetting but with the inductance 17 and the capacities 18 and 25 out ofcircuit, the effective input impedance of the tube 13 is high relativeto the impedance of the secondary winding of transformer 16 at lowfrequencies, but at the higher frequencies of the voice range thecapacity between the tube electrodes and the capacity within the coilitself have an appreciable effect. For these reasons the transformerpresents an inductive reaetance to the line in the lower part of thevoice range of frequencies and a capacitive reactance in the upper partof the voice frequency range. If no compensation for the effects ofthese reactances is provided, the repeater may give a' desired gain inthe middle portion of this frequency range and yet the transmission mayfall off considerably at the upper and lower parts of the range asinstaneed in the curve 9 of Fig. 2, with resulting distortion of thespeech signals. This would also re sultin poortransmission of ringingcurrents which in practice usually have a low frequency, as for example,135 cycles per second. Therefore, as disclosed in the patents of W. L.Casper, Nos. 1,530,648 and 1,530,649 issued March2et, 1925, there isprovided in series with the primary winding 15 the inductance 17 havingsuch a valuethat this inductance (and the leakage inductance of thetransformer where the leakage inductance is of a material value) willresonate with the capacitive reactance described above at a frequcncy inthe neighborhood of the upper part of the voice frequency range andthereby, as indicated by curve 9' of Fig. 3, prevent the transmissionfrom materially falling off at the higher speech frequencies andfurther, as disclosed in the patent of P. H. Pierce, No. 1,530,613,issued March 24, 1925, the condenser 18 is provided to annul theinductive reactance of the transformer at frequencies in the lower artof the voice range, the action of this con enser being to increase thegain of the repeater at the lower frequencies of the voice range, asindicated by a comparison of the curves 9 and 9 of Fig. 2, so that thegain frequenc characteristic of the repeater will'not fa ofi unduly atthese low frequencies (although at still lower, frequencies the gainwill of course be diminished, instead of increased, by the cone denser18).-

gain setting of the repeater of Fig. 1 when the inductance 17 and thecapacity 25 are not in circuit, it appears that as the contact.

quencies of the speech frequency range to be lowered less than the gainat lower frequencies is reduced as indicated by comparison of curves 9,8 and 7, and that after this movement of contact 20 has progressedpasttap 7 the gain at the higher frequencies of the voice range becomesgreater than the gain at lower frequencies, as instanced in curves 6, 5,4, 3 and 2, this latter effect being due apparently to the approachtoward the higher speech frequencies of the frequency of resonance ofthe leakage inductance of the transformer with the input capacity of thetube and the capacity between the winding turns of the transformer..Thus, while speech transmission may be practically distortionless whenthe contact 20 is on tap 7, the repeater may distort considerably atother gain settings.

As noted above, the distortion for the highest gain setting may beovercome by inserting inductance 17 in circuit, as indicated by curve 9-of Fig. 2, the resonance condition which makes curve 9- horizontalpractically throughout the length of the curve being analogous to thatwhich makes curve 7 horizontal throughout its length. However, after theinsertion of inductance 17 the distortion for low gain settings willprobably be even worse than before, the excess of the gain at highfrequencies over the gain at low frequencies being increased. To reducethe distortion for low gain settings, the con denser 25 is connected incircuit. If the capacity of condenser 25 remains constant, as thecontact 20 is moved from high voltage to low voltage taps the apparentcapacitive reaetance of this condenser as seen from the primar Windingof the transformer varies inversely as the square of the ratio of thenumber of secondary turns across which the condenser is connected to thenumber of turns in the primary-winding of the transformer; and thisvariation of apparent capacitive reactance tends to compensate-for thevariation of the apparent input capacitive reactance ofthe tube as seenfrom the primary winding of the transformer, this latter apparentcapacitive reactance varying inversely as the square of the ratio of thenumber of secondary turns across which it is connected to the number ofprimary turns of the transformer. If the capacity of condenser 25 is notto be varied, this condenser should have a capacity somewhat greaterthan the input capacity of the. tube 13, rather than equal to the in- 7put capacity of the tube as might/be expected Considering now the effectof changing the on first thought for if the two capacities are equal,then when the contact engages the middle of the secondary winding of thetransformer there will be substantially no current through the conductor21 the drop across condenser 25 being practical equal to that across theinput capacity of t e tube since the negative grid potential frombattery C insures. that the'resistance of the tube is of the order ofinfinity), and the two capacities will in effect he in series across thesecondary winding, so that their combined reuctance presented tothe'secondar winding will be twice the reactance whic the input'capacityof the tube presents-to the secondary winding in the highest gainsetting of the repeater.

However, the capacity of condenser 25 may be varled as the setting ofcontact 20 is changed, where it is desired to reduce distortion to aminimum for the various gain settings. Moreover, a close approach todistortionless transmission for the various-gain settings may beobtained with automatic variation of the capacity of the compensatingcondenser in response to movement of the gain settlng contact, one'means for accomplishing this being indicated in Fig, 4 wherein theparts are the same as in Fig. 1 except that a contact 20 and a condenser25 connected by a shaft have replaced-the contact .20 and condenser 25.The condenser 25 comprises a fixed semi-circular plate 36 connected tothe grid of the tube by a con-' ductor 37, and also comprises a plate 38attached to and movable with the shaft'35 which moves contact 20 overthe tap conductors 1 to 9. The condenser 25 may have its plates soshaped, or may be otherwise so designed, as to have the requisite amountof capacity to perform its compensatin function with a high degree ofaccuracy 1n each operative position of contact 20. As shown in Fig. 4,the voltage between any two adj acent taps may be the same, and theoutline of plate 38 is an approximately Archimedean spiral, so that ascontact 20 is moved counterclockwise from the position shown the rate ofdecrease of the capacity of condenser 25 with the angular displacementof contact 20 increases from a minimum, slow- -ly for some time butalways more and more rapidly until the contact 20" and the plate '38have moved through 180. When the contact 20 is moved from tap 9 to tap 5theapparent impedance of the input capacity of the tube as seen from theprimary win ing of the transformer increases in the ratio of 1 to 4, andin order to compensate for this 1 increase the apparent impedance of thecondenser 25 as seen fromthe, rimary winding of the transformer when t econtact 20 is on tap 5' should be approximatel four thirds or theapparent impedance t at the input ca acity of the tube would have wereit seen our the primary winding of the transformer with the contact 20on tap 9.

That is, when contact 20 is on ta 5, the impedance of condenser 25shouldbe equal to one third of the impedance of the input capacity of thetube, which means that the capacity of the condenser should then beequal to three times the input capacity of the tube. As the contact 20approaches very close to the zero gain setting, the value of thecapacity of condenser 25' should 'of course closely approach the valueof the input capacity of the tube, since the apparent input capacity ofthe tube as seen fr m the primary winding of the transformer is negli-'gibly small for such a setting of contact 20.

Instead of connecting an automatically variedcompensating condenserbetween tap 9 and the grid of the tube, an automatically variedcompensating condenser may be connected across the grid and filament ofthe tube as shown at 25 in Fig. 5, which is otherwise like Fig. 4 exceptthat the con-- deanspiral, and as contact 20 is moved counterclockwisethrough 180, from the position shown, the capacity of condenser 25increases from zero to a maximum, the rate of increase with angulardisplacement, being relatively slow at firstand increasing throughoutthe 180 displacement. hen the contact 20 is on tap 5 the capacity ofcondenser 25 should be approximately three times the input capacity ofthe tube, as explain'ed for the circuit of Fig. 4; but when the contact20 is in the lower gain settings the capacity of condenser 25 should belarge, and the capacity necessary will depend upon how low a voltage itis desired to tap from the transformer, or in other words how low a gainit is desired toobtain at the lowest gain setting of the repeater. V

The requisite capacity of the compensating condenser may be reduced byemploying a condenser arrangement. such as is shown in 6, which isotherwise like Figs. 4 and 5. In Fig. 6 a compensating condenser 25comprises a fixed plate 45 connected to the filament of tube 13,'andalso comprises a plate 46 connected to tap 9 by a conductor 47, theplate 46 being rotatable by the shaft 35 which engages a v gainadjusting contact 20 with taps 2 to The outline of plate 46 isapproximately an Archimedean spiral,

and as contact 20 is rotated counter-clockwise through from the positionshown,

the capacity ofcondenser 25 increases from zero' to a maximum, the rateof increase Fig. 7 is like Fig.5 except that instead of the condenser 25of Fig. 5, a separate condenser unit 25 is employed for each position ofa gain adjusting contact 20, whichcorresponds to the gain adjustingcontact 20 of Fig. 5, the contact 520 connecting one pole of theappropriate condenser unit to whichever one of the taps 2 to 9 happensto be in engagement with the contact. The condensers 25 have differentvalues,'the requisite value of the particular one of these condenserswhich is in use for any given gain setting of the repeater being thesame as the requisite value of the condenser 25 of Fig. 5 for the samegain setting.

In circuits such as those of Figs. 1 and 4: to 7, it is desirable toavoid the introduc tion of excessive capacities due to leads andswitching means, and Fig. 8 shows a struc-- The trans-.

ture which attains this end. former 16 and a housing 51 therefor aremounted on a base 50. The housing carries a condenser 25 which comprisesupper and lower nonconducting plates 55 and 56, respectively, connectedby upright members 57. On the plate 55 are mounted fixed con.- tactssuch as contacts 1 to 9, only one of 'these contacts, 5 being shown;Short tap conductors from the transformer 16 lead 'to these contactssuch as 5, one of these tap conductors being indicated at 58. A confact20 may be rotated by a shaft to engage the various contacts such as 5,the shaft having hearings in the plates 55 and 56. Fixed condenserplates of conducting material are mounted. on the members 57, andcondenser plates 61 of conducting material are mounted on shaft 35' torotate therewith, the plates 60 and 61 being so shaped or related thatthe rotation of shaft 35 varies the capacity of the condenser 25 in thedesired manner, as for instance in the manner in which the capacity ofthe condenser 25*, 25 or 25 is varied by rotation of shaft 35. Thetransformer and condenser of Fig. 8 may be connected in any circuits forwhich they are suited. For instance, they may be arranged former 16 andthe condenser 25, 25 or 25 are arranged in those circuits.

The straps interconnecting the several fixed plates 60 and movableplates (51 of condenser 25 have been omitted in Fig. 8 for the sake ofclarity, and the interconnections betweenfixed and movable plates 60 and(31 and the contact brush 20 and contacts 1 and 9 where they may occurhave also been omitted for the-same reason and because of thedifferences in the connections of Figs. 4, 5 and 6.

' Although the invention has been described I in circuits ofv .the typesshown in Figs. 4 to 6 as the trans mission of currents in the voicefrequency range, it is not restricted to transmission of suchfrequencies, for its principles are applicable also to the transmissionof'currents of other frequencies. It may be realized in variousembodiments differing from the specific forms depicted, without departing from the scope of the appended claims.

The invention claimed is:

1. A repeating circuit comprising an electron tube, an input transformertherefor having an inductance effectively in series with a winding ofsaid transformer for resonating with the input capacity of the tube andthe capacity between the winding turns of the transformer at a frequencyin the neighborhood of a frequency to be repeated, and a condenserproviding a capacity effectively across the secondary winding of saidtransformer of such magnitude as to materially lower the gain of therepeater circuit at the frequency of said resonance.

2. A circuit for repeating currents of a frequency range adequate forspeech transmission comprising a space discharge amplifying devicehaving input electrodes, an input transformer for said device having awinding provided with taps for connection to one of said inputelectrodes whereby different gain settings for said circuit may beobtained, inductance effectively in series with a winding of saidtransformer and of such value as to decrease the distorting ef-.

fect of said circuit on the higher. frequencies to be transmitted forthe higher gain said transformer of such value as to decrease.

the distorting effect of said circuit on the higher frequencies tobe'transmitted at the lower gain settings of said circuit.

3. A circuit for repeating currents of a frequency range adequate forspeech transmission, said circuit comprising an electron tube, an inputtransformer therefor having an inductance effectively in series with awinding of said transformer for resonating with the input capacity ofthe tube and the capacity between the winding turns of the transformerat a frequency in the neigh borhood of the upper frequencies of thevoice range. and a condenser providing a capacity effectively acrossthe. secondary winding of said transformer for controlling the gain ofsaid circuit at frequencies at least as high as a frequency in theneighborhood of the upper frequencies of the voice range.

4. A repeaterfor currents of a frequency range adequate for speechtransmission, said repeater comprising an electron tube having inputelectrodes, an input transformer for said tuhe having a winding providedwith taps for connection to one of said'electrodes,

' a condenser for providing capacity effecgain 0 tively across saidwinding, and means for varying the connection of said electrode to saitaps and for insuring that the value of capacity which is providedeffectively across said wlnding by said condenser is simultaneouslg sovaried as to equalize the repeater anges due to the variation of theconnection of said electrode to said taps, over the upper part of thefrequency range to be transmitte a 5. In'combination, an electron tubehaving input electrodes, an input transformer therefor having awindingprovided with taps'for connect-ion to one of said electrodes,

a condenser for providing capacity efl'ectively across said -winding,-and means for input capacity of said tu e across-saidwindvarying theconnection of said electrode to said taps and for simultaneousl ,so vaing said effective capacity provi ed by sa1d condenser as to compensatefor the variation of the. value of capacity provided b the inputcapacity of said tube effective y across said winding.

6. 'A circuit comprising an electron tube having an electrode, an nputtransformer therefor having a winding provided with taps, means foradjustabl connecting said electrode to said taps, an a condenser betweensaid electrode and a fixed oneof said such value as to compensate for"ariations of the effective 'capacit provided by the ing, as the.connection of said electrode to said .taps isvaried. 7.' A circuitcomprising an electron tube having two input electrodes, an inputtransformer for said tube, said transformer having a winding providedwith taps, means connecting one of said electrodes to one end of saidwinding, a condenser connected between the other of said electrodes andthe other end of said winding, and means for adjust-ably connecting saidother electrode to said taps to vary the gain setting of sand circuit,and for simultaneously varying the capacity of said condenser, "saidcondenser being designed with respect ,to said means so that itsvariation in capacity for a given change in said gain setting is prortioned.

to compensate for the 'varation 1n t e apparent input capacitivereactance of said tube 'with the change in gain setting tending to causedistortion in said circuit.

8. A circuit comprising havin an electrode, an input transformer thereorhaving a winding provided with vtaps, meansf for adjustably connectingsaid electrode to said taps, a variable condenser connection of saidelectrodeto said taps in such manner as to decrease the potential ofsaid electrode at a constant rate. I

9. In a circuit for repeating currents havinga wide frequency range, anelectric space discharge tube having input electrodes with an effectiveinput capacity therebetween, an

input transformer for said tube, said trans-- former having tapconductors, a contact, means movable :to engage said contact with saidtaps to vary the gain of said circuit, I

a variable condenser in circuit withsaid transformer and sa1d tube andmounted III immediate proximity to said transformer,

said condenser having its maximum'capacity of the order of saideffective input capacity of said tube, and means operable by said firstmentioned means to vary the capacity of said condenser as the setting ofsaid contact is changed, said condenser being designed with respect tosaid movable means so that its variation in capacity for a given changein gain setting is proportioned to compensate for the variation inapparent input capacitive reactance of said tube due to said change ingain setting whichtends tocause distortion in the repeated currents ofcertain frequencies.

an electron tube In witness whereof, I hereunto. subscribe as my namethis 25th day of May, A. D., 1923.

DONALD WHITING.

